Head suspensions are well known and commonly used within dynamic magnetic or optical information storage devices or drives with rigid disks. The head suspension is a component within the disk drive that positions a magnetic or optical read/write head over a desired position on the storage media where information is to be retrieved (read) or transferred (written). Head suspensions for use in rigid disk drives typically include a load beam that generates a spring force and that supports a flexure to which a head slider having a read/write head is to be mounted. The load beam includes a mounting region at a proximal end, a rigid region at a distal end, and a spring region between the rigid region and the mounting region for providing the spring force. Head suspensions are normally combined with an actuator arm or E-block to which the mounting region of the load beam is mounted with a base plate so as to position (by linear or rotary movement) the head suspension, and thus the head slider and read/write head, with respect to data tracks of the rigid disk.
The rigid disk within a disk drive rapidly spins about an axis, and the head slider is aerodynamically designed to “fly” on an air bearing generated by the spinning disk. The spring force (often referred to as the “gram load”) generated by the load beam urges the head slider in a direction opposing the force generated by the air bearing. The point at which these two forces are balanced during operation is the “fly height” of the head slider.
The flexure typically includes a slider bond pad to which a head slider is attached. The flexure attached to the load beam provides a resilient connection between the slider and the load beam, and permits pitch and roll motion of the head slider and read/write head as they move over the data tracks of the disk in response to fluctuations in the air bearing caused by fluctuations in the surface of the rigid disk. Head suspension flexures can be provided in numerous ways, including designs in which the load beam and flexure are formed integrally with one another (a two-piece design comprising the base plate and the integral load beam/flexure) and designs in which the flexure is a separate piece from the load beam (a three-piece design comprising the base plate, the load beam and the separate flexure). One three-piece design includes a flexure having a resilient tongue and two resilient spring arms. The head slider is supported on the resilient tongue (i.e. the slider bond pad), which is in turn supported between the spring arms. The spring arms are connected to a flexure mounting region, which is in turn connected to the load beam. The gram load provided by the spring region of the load beam is transferred to the flexure via a dimple that extends between the rigid region of the load beam and the flexure. The spring arms allow the tongue of the flexure to gimbal in pitch and roll directions to accommodate surface variations in the spinning magnetic disk over which the slider is flying. The roll axis about which the head slider gimbals is a central longitudinal axis of the head suspension. The pitch axis about which the head slider gimbals is perpendicular to the roll axis. That is, the pitch axis is transverse to the longitudinal axis of the load beam, and crosses the roll axis at or around the head slider.
In order to store and retrieve data from magnetic or optical disks on which data is densely packed, it is necessary for the head slider to fly closely above the surface of the spinning data disk (on the order of 0.1 μm) without colliding with the disk (“crashing”). Further, because of the dense packing of data on magnetic or optical disks, it is important for the read/write head attached to the head slider to be able to read from or write to a relatively small area or spot on the disk.
In relation to this, important performance characteristics of a head suspension include the fly height at which the head suspension positions a head slider and the positional orientation of the head slider in relation to the spinning data disk when the head suspension is in a “loaded” state (i.e. under the influence of the balanced forces created by the spring force and the air bearing). The head slider is designed to fly at a predetermined orientation, typically with its bottom surface or a portion thereof arranged generally parallel with the surface of the disk, and this orientation is often referred to as the “dynamic attitude”.
When the head suspension is not actually flying over a spinning disk, the loaded state of the head suspension can be simulated by applying a force in the same direction as the air bearing force at a point on the head suspension other than to the slider bond pad where the head slider would be attached (or, if the slider is attached, other than to the head slider). This force is applied to lift the slider bond pad to its loaded position at the fly height. The orientation or attitude of the slider bond pad under this simulated loaded state is referred to as “static attitude.” The difference or bias between the dynamic attitude and the static attitude can be measured for a given head suspension so that a measurement of the static attitude, which can be an easier measurement to make than dynamic attitude, can be used to determine dynamic attitude for a given head suspension. In other words, a head suspension typically has a predetermined static attitude that can be used to assess the dynamic attitude of a head slider attached to the head suspension during normal operation of a disk drive.
Static attitude of a head slider bond pad can be measured with reference to pitch and roll axes of the head suspension. Roll is a rotation of the slider bond pad about the roll axis of the head suspension and pitch is a rotation of the slider bond pad about the pitch axis of the head suspension. Deviations from the desired static attitude about the roll axis can be referred to as roll errors, while deviations from the desired head slider attitude about the pitch axis can be referred to as pitch errors. Pitch and roll errors in static attitude can be caused by manufacturing variations of the head suspension, handling of the head suspension and related components during and after manufacturing, or contamination of the head suspension by airborne foreign matter.
If pitch and/or roll errors exist in the static attitude of a head suspension, there is a greater possibility that errors will exist in the dynamic attitude of the head slider, and that the head slider might crash into the disk. Such crashes are generally undesirable. Further, errors in static attitude of the head slider can cause the read/write head to be out of proper orientation to the surface of the disk or further from the disk surface than it is designed to be. As such, the read/write head may not be able to “focus” on as small an area or spot on the disk as is necessary to efficiently transfer data to or from the disk. This can degrade disk drive performance.
In addition, it may be desirable to adjust the static attitude of a head suspension from a nominal orientation to impart a desired pitch and/or roll bias into the head suspension. In so far as these biases represent incremental changes in pitch and roll static attitude imparted to the head suspension, these too can be viewed as pitch and roll corrections, and the differences between nominal and desired attitude can again be referred to as pitch and roll errors.
Because of the importance of correct head slider attitude, various methods exist for correcting pitch and roll errors to obtain appropriate static attitude. Such methods are disclosed in, for example, U.S. Pat. No. 5,682,780, issued Nov. 4, 1997 to Girard for “Gram Load, Static Attitude And Radius Geometry Adjusting System For Magnetic Head Suspensions”; U.S. Pat. No. 5,608,590, issued Mar. 4, 1997 for “Gimballing Flexure With Static Compensation And Load Point Integral Etched Features”; and U.S. Pat. No. 5,729,889 issued Mar. 24, 1998 for “Method Of Mounting a Head Slider To a Head Suspension With Static Offset Compensation”. Each of these applications and patents are commonly owned by the assignee of the present application and are fully incorporated herein by reference for all purposes.
One method of correcting errors in the static attitude involves mechanically twisting and/or bending the head suspension to alter the profile of the load beam. In such a method, the profile of the load beam can be altered to support the flexure at an attitude to the disk surface that compensates for any errors in the static attitude of the head suspension. That is, the load beam can be bent about an axis perpendicular to the longitudinal axis of the load beam to account for pitch errors in the static attitude of the head suspension. The load beam can also be twisted about its longitudinal axis to account for roll errors in the static attitude. Similarly, the flexure can be mechanically bent and twisted to try to correct static attitude errors.
Adjusting the head suspension in this way, however, can negatively affect other head suspension parameters, such as the fly height, gram load, and overall resonance profile of the head suspension. In particular, bending the head suspension to affect pitch static attitude also affects gram load, resonance, and head lift height, while twisting the head suspension to correct roll static attitude affects head suspension resonance and introduces vibratory motion in the off-track direction, which can negatively impact disk drive performance. Such mechanical adjustments can also be undesirable due to the amount of forming required to get an appropriate adjustment in static attitude. Moreover, it can be difficult to properly mechanically deform head suspension components due to their relatively small size, which limits the size and operating room for tools used to perform the mechanical adjustments.
Further, it is known to form electrical leads on the load beam for carrying electronic read/write signals from the read/write head to data electronics. It can be difficult to mechanically alter the profile of the head suspension without adversely affecting the electrical leads. Electrical leads can also make it difficult to engage tooling with the suspension components to make a static attitude adjustment.
Mechanically adjusting head suspension static attitude can also be inefficient in terms of the precision with which static attitude can be corrected, and in the cycle time it takes to correct the static attitude of an individual head suspension. It is a general industry trend to more densely pack information onto a magnetic disk so as to be able to make disk drives smaller without impacting the amount of data that can be stored in the drive. This necessitates smaller disk drive components, including smaller head suspensions. As data density increases and head suspension size decreases, it becomes increasingly important that the head slider be at the desired attitude when at the fly height, and acceptable tolerances on head suspension static attitude are reduced. Current methods for correcting deviations in static attitude thus may not provide sufficiently fine corrections to account for decreased static attitude tolerances. This can be particularly true when the static attitude correction occurs in individual components of the head suspension prior to mounting them together, since additional errors may be introduced in the mounting process.
Moreover, the conventional static attitude adjustment methods described above are typically performed along with head suspension load beam adjustments to gram load, and mixing the two adjustment processes can create longer feedback loops in the manufacturing process, which increases part cycle time. Mixing the two adjustment processes can also lead to less accurate static attitude adjustments, which negatively impacts part yield.
There is a continuing need to develop more efficient methods for correcting pitch and/or roll errors in head suspension static attitude. A method that provides precise error corrections in a timely fashion, and that can be achieved without significant impact on other performance criteria of the head suspension is highly desirable.